1. Field of the Invention
The present invention relates to a technique for measuring, from an aircraft in flight, wind turbulence forward of the flight path of the aircraft, and for measuring the precise airspeed of the aircraft, and relates to a system thereof.
2. Description of the Related Art
An aircraft flying through the atmosphere is continually subject to wind effects, and an abrupt change in the wind is one principal cause of air crashes. As a result of a pilot having prior knowledge of flight path frontward wind shear, clear air turbulence, down burst, for example, a contribution can be made to flight safety in that the pilot can then alert passengers by means of a communication regarding wind turbulence, evade wind turbulence, and pilot the aircraft in such a manner that violent aircraft body movements are reduced. Use of measured information that involves transmitting same to a control system such as an auto-pilot control system is also conceivable. On the other hand, although normal flight tests are performed in the development and improvement of aircraft, precise airspeed measurement is indispensable in order to obtain basic characteristic data in the course of such flight tests.
Methods from the prior art of investigating wind turbulence and measuring airspeed include the following:
1) Wind Shear Warning Device
There are two kinds of wind shear warning device, namely: a device constituted to calculate wind, using an airspeed sensor, which is mounted on the aircraft body, from a comparison with inertial speed, to estimate wind shear from this difference in speed; and a device constituted to utilize electric waves to measure frontward wind turbulence.
2) Ground-Based Observation Device
This device permits observation of wind in an aircraft flight path by means of the ground-based installation of a remote sensor that observes the wind in the sky above, and systems employed in accordance with this object include systems utilizing sound waves, systems utilizing electric waves, and systems utilizing light waves, among which a system utilizing light waves is called a xe2x80x9cwind measurement lidarxe2x80x9d.
3) Pitot Tube
This involves the use of a Pitot tube mounted on an aircraft body to measure the total pressure and static pressure of the air to thereby seek the airspeed from the impact pressure constituted by the difference between the total pressure and static pressure of the air. The Pitot tube is the most widely used aircraft airspeed sensor.
However, air flow measured by means of these conventional devices is in the direction of travel alone. Since air flow measured by means of a conventional Pitot tube or electric waves is in the direction of travel alone, is not possible to perform measurement of three-dimensional wind turbulence. Also, there is a problem that awareness using a wind shear warning system is difficult. In other words, with regard to some wind shear warning devices mounted on large aircraft, in emitting a warning hurriedly without prior notice, not only is awareness delayed, but it is also impossible to confirm whether such a warning is reliable. In addition, material permitting a judgement of what measures are to be taken, is limited. Further, when a cylindrical lens, which is ordinarily employed for an optical system of a wind measurement lidar, is mounted on an aircraft, a large protrusion by this cylindrical lens leads to large aerodynamic and structural effects, meaning that there has been the problem of there being a great number of limitations placed on mounted instruments and on the locations of these mounted instruments. Furthermore, a Pitot tube has a structural shortcoming of not being employable within a low velocity range. In other words, since the impact pressure measured using a Pitot tube is proportional to two times the airspeed, in a low velocity range, there is a large measurement error. Consequently, the velocity at which a Pitot tube can be utilized is normally 20 to 30 m/s or more. In addition, in cases of low velocity or when the air flow direction differs greatly from the aircraft body axis, measurement is not possible. Also, an airspeed sensor that is mounted directly on the aircraft body, such as a Pitot tube, for example, produces a measurement error resulting from disruption of the air flow by the aircraft body itself. This error is referred to as a position error, and such a position error is exhibited by a Pitot tube.
An object of the present invention is to resolve the numerous problems exhibited by conventional devices like those described above, in other words, to provide a measurement system capable of measuring three-dimensional wind turbulence, and which, instead of issuing sudden warnings without prior notice like those of a conventional wind shear warning system, performs inquiries by means of a constitution permitting confirmation in advance of whether or not a given warning is reliable and straightforward judgement of what measures are to be taken. Further, such a measurement system exhibits limited aerodynamic and structural effects when mounted on an aircraft, and is capable of measurement without the production of a position error, even in cases in which the velocity is equal to or less than 20 to 30 m/s, at which velocity a Pitot tube is incapable of measurement, and in cases where the air flow direction differs greatly from the aircraft body axis.
The wind turbulence prediction system of the present invention adopts a system that measures the speed of remote three-dimensional air flow by mounting a laser wind speed indicator utilizing the Doppler effect on an aircraft, irradiating laser light while scanning same in a cone shape, and then receiving scattered light from wind turbulence regions forward of an aircraft body in flight. Also, by considering the effects on the aircraft body exerted by a vertical wind and a fore and aft wind, measured three-dimensional air flow information is converted to a vertical wind alone and then displayed in simplified form in two dimensions, and wind turbulence is expressed through breakdown of same into turbulent flow strength and average wind. Also, when measured air flow information is communicated to the pilot, a turbulence position is displayed, not taking distance as a reference [of the turbulence position], but instead taking, as a reference, the time that elapses before the turbulence is encountered, and the ease of mounting, of a cylindrical optical system of a wind measurement lidar, is improved by cutting away a section of the cylindrical optical system.